--- In VacuumX@..., Hans Summers <Hans.Summers@t...>
I suspect the problem with Tungsten might be oxidation. H P
I would think that once proper vacuum has been reached there won't
be enough o2 left to cause any appreciable wear.
Seems that for aluminum the classic format is that of the heavy
gauge spiral tungsten filament. Aluminum in particular will alloy
with the tungsten prior to evaporation. Choice of wire size is
somewhat important as if your gauge is too fine the AL will dissolve
through the filament and casue it to break.
The site www.lesker.com contains TONS of useful vacuum information,
including suggested filament materials to be used with target
evaporants. The chart at:
irements_Boats7.cfm?
CFID=218535&CFTOKEN=45377807§ion=tspttboats&init=skip
describes the voltage, amperage, power, max temperature relations
for their thermal evaporation sources.
The old evap I'm resurrecting uses a tungsten 'boat', specifically
the EV31A010W model, at:
oat_EVS29000_35000.cfm?
CFID=218535&CFTOKEN=45377807§ion=tsboats&init=skip
You can't beat the price - each boat is $5 or such. Peak
temperature is listed at 1800 C.
Friedrichs has
used tungsten light bulb filaments in homemade triodes etc. See
his book
Instruments of Amplification
Ohho sounds like I'll have to buy this book!
-Bill
